Gradient‐Interpenetrating Polymer Networks in 3D Printed Lattices for Tunable and Enhanced Energy Absorption

Abstract 3D printing provides the potential to enhance mechanical properties by fabricating complex structures with diverse materials; however, most high‐resolution 3D printing techniques require custom printers to incorporate multiple materials and/or result in poor material interfacial bonding. Here, energy absorption properties are enhanced with 3D lattice structures fabricated via vat photopolymerization comprising multiple materials forming a gradient‐interpenetrating polymer network (gradient‐IPN). The gradient‐IPN is incorporated by swelling the 3D printed elastomeric lattice in a photoresin that yields a stiff shell‐soft core structure. This straightforward post‐3D printing technique delivers an unprecedented degree of structural property customization through polymer gradients in lattice struts with shells of tunable stiffness and flexible elastomeric cores to achieve a broad continuum spectrum of mechanical properties within one simple system. The gradient aids in the distribution of stress and limits fracture between materials typically observed in multimaterial lattices. The gradient‐IPN lattices are fully recoverable and exhibit over 4 to 33 times higher toughness after compression, compared to copolymer (same composition as the gradient‐IPN) or purely elastomeric lattices, respectively. This highly versatile approach to modifying 3D printed lattices yields the unique combination of load bearing capabilities with viscoelasticity desirable for high performance materials in impact protection.